Abstract. Aerosol loading over Interior Alaska displays a strong seasonality, with
pristine conditions generally prevailing during winter months. Long term
aerosol research from the University of Alaska Fairbanks indicates that the
period around April typically marks the beginning of the transition from
winter to summer conditions. In April 2008, the NASA-sponsored "Arctic
Research of the Composition of the Troposphere from Aircraft and
Satellites" (ARCTAS) field campaign was conducted to analyze incursions of
aerosols transported over Alaska and the Canadian North. In and around
Fairbanks, Alaska, data concerning aerosol characteristics were gathered by
polarization (0.693 μm) lidar, DRUM Impactor sampler, and balloon-borne
optical particle counter. These data provide information on the vertical
distribution and type of aerosol, their size distributions, the chemical
nature of aerosol observed at the surface, and timing of aerosol loading. A
detailed synoptic analysis placed these observations into their transport
and source-region context. Evidence suggests four major aerosol loading
periods in the 25 March–30 April 2008 timeframe: a period during which
typical Arctic haze conditions prevailed, several days of extremely clear
conditions, rapid onset of a period dominated by Asian dust with some smoke,
and a period dominated by Siberian wildfire smoke. A focused case study
analysis conducted on 19 April 2008 using a balloon-borne optical particle
counter suggests that, on this day, the majority of the suspended
particulate matter consisted of coarse mode desiccated aerosol having
undergone long-range transport. Backtrack trajectory analysis suggests aged
Siberian wildfire smoke. In the last week of April, concentrations gradually
decreased as synoptic conditions shifted away from favoring transport to
Alaska. An important result is a strong suggestion of an Asian dust
incursion in mid-April that was not well identified in other ARCTAS
measurements. The lidar and OPC-sonde unambiguously discern aerosols height
stratification patterns indicative of long range transport. Identification
of a dust component is suggested by DRUM sampler results, which indicate
crustal species, and supported by synoptic and trajectory analysis, which
indicates both a source-region lifting event and appropriate air-mass
pathways.